1. Technical Field
The present invention relates to an optical disk drive, and more particularly to reproduction processing performed when warpage is present in an optical disk.
2. Related Art
A reproduction rate of an optical disk is appropriately optimized according to a reproducing state. For instance, when data are reproduced by means of; for example, equipment incorporated in or connected to a personal computer, the data must be reproduced as fast as possible, and hence a reproduction rate is increased. Further, at the time of playback of a video or music, a transfer rate is determined. Therefore, a reproduction rate which is faster than the predetermined transfer rate is not required. Even if data can be reproduced at high speed, the reproduction rate is maintained at a low rate in consideration of tranquility.
In the meantime, when side-to-side runout or mass eccentricity is present in an optical disk or when meandering of a track, or the like, is present, data cannot be read when reproduction is performed at a high rate, thereby resulting in occurrence of an error. In consideration of this, decreasing the reproduction rate has been proposed.
JP 10-40640 A discloses that, when excessive vibrations arise in the middle of a disk being subjected to high-speed production or when mass eccentricity of predetermined levels is detected, the rotational speed of the disk is reduced to perform reproduction at a low rate, thereby diminishing vibrations.
JP2002-251844 A discloses that, when a poorly-readable area, such as a defect, is detected, data recorded in the poorly-readable area are read without decreasing the rotational speed of the optical disk by means of switching a cutoff frequency of a high-pass filter.
JP 2003-297007 A discloses that the rotational speed of a disk is set to the minimum rotational speed when reproduction of the disk is started and that control is performed so as to increase the rotational speed of the disk stepwise until a read error arises, whereby, when compared with a case where the rotational speed is reduced from the maximum rotational speed, a time elapsed before reproduction is shortened.
JP 2004-281041 A discloses that, when data are recorded/reproduced in or from an optical disk that rotates at predetermined equiangular velocity, occurrence of an error during recording/reproduction of data is monitored and that, when occurrence of an error during recording/reproduction of data is detected, the rotational speed of the optical disk is controlled so as to come to equiangular velocity which is lower than the predetermined equiangular velocity, thereby shortening a time required to record/reproduce data.
In any of the related-art techniques, when a poorly-readable area is detected, the rotational speed of the disk is indiscriminately reduced as compared with a case where the poorly-readable area is not detected. However, under such a control method for indiscriminately reducing rotational speed, data cannot be read when warpage is present in an optical disk.
When an optical disk drive is equipped with a lens tilting device, the essential requirement is to control tilt of a lens in conformance to warpage in the optical disk. However, incorporation of the lens tilting device leads to an increase in the number of components, an increase in cost, and an increase in the size of the optical disk drive or an optical pickup. Accordingly, the ability to address warpage in an optical disk without incorporation of a lens tilting device is desirable.